1/*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.io;
18
19import static com.google.common.base.Preconditions.checkArgument;
20import static com.google.common.base.Preconditions.checkNotNull;
21
22import com.google.common.annotations.Beta;
23import com.google.common.base.Charsets;
24import com.google.common.base.MoreObjects;
25import com.google.common.collect.Lists;
26
27import java.io.IOException;
28import java.io.InputStream;
29import java.io.OutputStream;
30import java.net.URL;
31import java.nio.charset.Charset;
32import java.util.List;
33
34/**
35 * Provides utility methods for working with resources in the classpath.
36 * Note that even though these methods use {@link URL} parameters, they
37 * are usually not appropriate for HTTP or other non-classpath resources.
38 *
39 * <p>All method parameters must be non-null unless documented otherwise.
40 *
41 * @author Chris Nokleberg
42 * @author Ben Yu
43 * @author Colin Decker
44 * @since 1.0
45 */
46@Beta
47public final class Resources {
48  private Resources() {}
49
50  /**
51   * Returns a {@link ByteSource} that reads from the given URL.
52   *
53   * @since 14.0
54   */
55  public static ByteSource asByteSource(URL url) {
56    return new UrlByteSource(url);
57  }
58
59  /**
60   * A byte source that reads from a URL using {@link URL#openStream()}.
61   */
62  private static final class UrlByteSource extends ByteSource {
63
64    private final URL url;
65
66    private UrlByteSource(URL url) {
67      this.url = checkNotNull(url);
68    }
69
70    @Override
71    public InputStream openStream() throws IOException {
72      return url.openStream();
73    }
74
75    @Override
76    public String toString() {
77      return "Resources.asByteSource(" + url + ")";
78    }
79  }
80
81  /**
82   * Returns a {@link CharSource} that reads from the given URL using the given
83   * character set.
84   *
85   * @since 14.0
86   */
87  public static CharSource asCharSource(URL url, Charset charset) {
88    return asByteSource(url).asCharSource(charset);
89  }
90
91  /**
92   * Reads all bytes from a URL into a byte array.
93   *
94   * @param url the URL to read from
95   * @return a byte array containing all the bytes from the URL
96   * @throws IOException if an I/O error occurs
97   */
98  public static byte[] toByteArray(URL url) throws IOException {
99    return asByteSource(url).read();
100  }
101
102  /**
103   * Reads all characters from a URL into a {@link String}, using the given
104   * character set.
105   *
106   * @param url the URL to read from
107   * @param charset the charset used to decode the input stream; see {@link
108   *     Charsets} for helpful predefined constants
109   * @return a string containing all the characters from the URL
110   * @throws IOException if an I/O error occurs.
111   */
112  public static String toString(URL url, Charset charset) throws IOException {
113    return asCharSource(url, charset).read();
114  }
115
116  /**
117   * Streams lines from a URL, stopping when our callback returns false, or we
118   * have read all of the lines.
119   *
120   * @param url the URL to read from
121   * @param charset the charset used to decode the input stream; see {@link
122   *     Charsets} for helpful predefined constants
123   * @param callback the LineProcessor to use to handle the lines
124   * @return the output of processing the lines
125   * @throws IOException if an I/O error occurs
126   */
127  public static <T> T readLines(URL url, Charset charset,
128      LineProcessor<T> callback) throws IOException {
129    return asCharSource(url, charset).readLines(callback);
130  }
131
132  /**
133   * Reads all of the lines from a URL. The lines do not include
134   * line-termination characters, but do include other leading and trailing
135   * whitespace.
136   *
137   * <p>This method returns a mutable {@code List}. For an
138   * {@code ImmutableList}, use
139   * {@code Resources.asCharSource(url, charset).readLines()}.
140   *
141   * @param url the URL to read from
142   * @param charset the charset used to decode the input stream; see {@link
143   *     Charsets} for helpful predefined constants
144   * @return a mutable {@link List} containing all the lines
145   * @throws IOException if an I/O error occurs
146   */
147  public static List<String> readLines(URL url, Charset charset)
148      throws IOException {
149    // don't use asCharSource(url, charset).readLines() because that returns
150    // an immutable list, which would change the behavior of this method
151    return readLines(url, charset, new LineProcessor<List<String>>() {
152      final List<String> result = Lists.newArrayList();
153
154      @Override
155      public boolean processLine(String line) {
156        result.add(line);
157        return true;
158      }
159
160      @Override
161      public List<String> getResult() {
162        return result;
163      }
164    });
165  }
166
167  /**
168   * Copies all bytes from a URL to an output stream.
169   *
170   * @param from the URL to read from
171   * @param to the output stream
172   * @throws IOException if an I/O error occurs
173   */
174  public static void copy(URL from, OutputStream to) throws IOException {
175    asByteSource(from).copyTo(to);
176  }
177
178  /**
179   * Returns a {@code URL} pointing to {@code resourceName} if the resource is
180   * found using the {@linkplain Thread#getContextClassLoader() context class
181   * loader}. In simple environments, the context class loader will find
182   * resources from the class path. In environments where different threads can
183   * have different class loaders, for example app servers, the context class
184   * loader will typically have been set to an appropriate loader for the
185   * current thread.
186   *
187   * <p>In the unusual case where the context class loader is null, the class
188   * loader that loaded this class ({@code Resources}) will be used instead.
189   *
190   * @throws IllegalArgumentException if the resource is not found
191   */
192  public static URL getResource(String resourceName) {
193    ClassLoader loader = MoreObjects.firstNonNull(
194        Thread.currentThread().getContextClassLoader(),
195        Resources.class.getClassLoader());
196    URL url = loader.getResource(resourceName);
197    checkArgument(url != null, "resource %s not found.", resourceName);
198    return url;
199  }
200
201  /**
202   * Given a {@code resourceName} that is relative to {@code contextClass},
203   * returns a {@code URL} pointing to the named resource.
204   *
205   * @throws IllegalArgumentException if the resource is not found
206   */
207  public static URL getResource(Class<?> contextClass, String resourceName) {
208    URL url = contextClass.getResource(resourceName);
209    checkArgument(url != null, "resource %s relative to %s not found.",
210        resourceName, contextClass.getName());
211    return url;
212  }
213}
214